Modulator



Dec. 27, 1949 MARKER 2,492,168

MODULATOR FiledApril 3, 1948 SQUARE WAVE PULSE AMI? IFECWF/tn mrm k i kmJ5 m E k k as /55 l a Q E I & k 8 RfFLfCTR V/ V2 v 0 o WME VOLTAGE I l lEEFZEC'TO/P VI 0 5 JNVENTOR. VOLT/76E THU/VA r. MARKER TTOFNEY PatentedDec. 27, 1949 I MODULATOR Thomas F. Marker, Bloomfield, N. J., alsignorto International Standard Electric Corporation, New York, N. Y., acorporation of Delaware Application April 3, 1948, Serial No. 18,812

'lClalms. 1

My invention relates generally to modulators and more particularly tomeans for applying si nal voltages to regulated or steady directcurrents in a communication system.

Electronic oscillator, amplifiers, and modulators invariably require ahigh voltage direct current source and, generally, this source mustsupply a fairly steady voltage to prevent undesired frequency drift,changes in gain, and the like. Some systems are so sensitive to thesevoltage changes that voltage regulators are placed between the sourceand the load. One regulator comprises a discharge device with thegrid-controlled space of the device connected in series with the loadand source, and with a feed-back circuit to apply voltages to the gridin phase opposition to voltage changes at the source to neutralize andhold steady the voltage at the load. Obviously, signal voltages cannotbe impressed on the direct current voltage of such a regulated sourcebecause the signals would be opposed and neutralized by the regulator.

One object of my invention is, accordingly, a signaling system in whichsignals may be effectively impressed on regulated direct current.

The generator of microwaves requires particularly well regulated directcurrent sources, the frequency of operation usually being responsive tosmall changes of electrode potential. The output of the so-called reflexoscillator, for example, will vary in frequency or even stop with smallchanges of potential of the reflector electrode and must be connected toa voltage regulator that will effectively protect the reflector fromvoltage changes. When rectified alternating current of commercial powerlines is used, both gradual and rapid fluctuations of line voltage mustbe reckoned with and regulators as well as the usual filters must beused. Yet, it is sometimes desirable to modulate the amplitude of directcurrent supplied to such oscillators while maintaining steady theunmodulated or reference value of the voltage.

Accordingly, a more specific object of my invention is a system formodulating with signals the amplitude of regulated voltages tooscillators, a still more specific object being the modulation .of thedirect current voltage applied to the refiection electrode of a reflexoscillator.

One embodiment of my invention comprises, essentially, a voltage sourceand a load such as an oscillator with a voltage regulator therebetween.The regulator contemplated comprises a gridcontrolled electron dischargedevice with the anode-cathode space connected in series with the sourceand with the grid coupled to the line and responsive to voltage changesat the load so that the impedance of the anode-cathode space may bechanged to compensate for changes in voltage at the source. A signalsource is also connected to the grid, and to prevent neutralization ofthe signal modulation intended for the load, a low pass filter isinserted between the grid and the point on the line from which the gridreceives its degenerative energy. Hence, the grid may respond to theslow line variations or low frequency changes below the cut-oilfrequency of the low pass filter, but will not respond to signalfrequencies feed-back from the line.

The above-mentioned and other featuresand objects of this invention andthe manner of attainin them will become apparent and the inventionitself will be best understood, by reference to the followingdescription of an emb0diment of the invention taken in conjunction withthe accompanying drawing, wherein:

Fig. 1 is a circuit diagram of one modulator of this invention, and

Fig. 2 are graphs showing the functional relation of important variablesof the circuit of Fig. 1.

For illustrating the principles of this invention, the simplerectangular signal wave is first considered, and the oscillator on whichthe signals are impressed is of the reflex type. It will be understoodas the description proceeds that both the signal source and the type ofoscillator may be changed in many ways without departing from the scopeof the invention. Further, the details of the voltage regulator circuitsmay be changed in various ways by those skilled in the art within theteachings here set forth. The oscillator l comprises a cathode 2, acontrol grid 3 and a pair of grids 4 and 5 in aligned openings in aresonant cavity structure 6. The cavity walls are toroidal and aresymmetrical about the aligned openings. The reflector electrode 1 isparallel to and is spaced a measured distance from the grids on the sideopposite th cathode. A relatively high voltage on the grids acceleratesthe electrons from the cathode to and through the grid openings. As theelectrons traverse the space between and near the grids, certain of theelectrons are accelerated still more and others are decelerateddepending on th times of arrival with respect to the time phase of thealternating electric field between the grids. This later effect tends tobunch the electrons. The bunches of electrons approaching the reflectorare decelerated by the negative reflector field, are stopped, and arereturned to the grid so that for a given initial velocity and electrodespacing the reflector voltage may be adjusted to cause the electronbunches to return to the grid at the proper time phase to give up muchof their kinetic energy to the electric field. Experience has shown thatoscillations may be maintained at a number of distinctly differentreflector voltages, the oscillations, always at or near cavityfrequency, being known as voltage modes. The range of tuning by thereflector voltage within any voltage mode is quite narrow and theoscillator is inactive at intermediate values of reflector voltage.

The voltage source and voltage regulator for the reflector, hereinaftermore fully described, may be adjusted to hold the reflector at preciselythe desired mode voltage, and the signal source in combination therewithwill vary the reflector voltage, in spite of the regulator for thevoltage source. Undulating and voice signals will frequency modulate theoscillator over a limited range, but with pulse signals of the properamplitude, the reflector voltage may be made to swing abruptly into andout of the mode voltage to turn the oscillator on and off. The pulses,further, may be modulated as to phase, frequency, or duration.

A commercial alternating current power source I is assumed and since therectifier and filter 9 may be any of the known types they need nospecific description. The positive and negative output leads I and H ofthe rectifier are connected, respectively, to the cathode 2 andreflector electrode 1 of the oscillator. In one lead, for example In, isserially connected the anodecathode space l2l3 of the electron dischargedevice It, the grid IS in the device conveniently controlling theanode-cathode impedance of the device. The voltage applied to the loadis sampled by the sliding contact it of a potentiometer i1 directlyacross the load, or if desired directly across the source. For greatersensitivity, the voltage at the contact i6 is first amplified in thepentode l8 and then applied to the grid I of the impedance device It.The pentode includesan anode IS, a cathode 2n and control grid 2| aswell as a screen and suppressor. The gaseous discharge tube 22 isconnected in the cathode circult of the amplifier to establish a fixedpotential for the cathode so that voltage changes at the grid of theamplifier will appear in amplified form at the anode and hence at thegrid of the impedance device. With the plate load resistor 23 connectedas shown the amplified voltages are inverted so that increased currentthrough the impedance tube and increased voltage at the potentiometercontact l6 and grid 2| means reduced voltage at the plate I9 of theamplifier and at the grid ii of the impedance tube.

According to a further and important feature of this invention, signalvoltages are also applied to the grid 15 of the impedance device. Theparticular signal source shown comprises a signal oscillator 24, of say900 to 1100 cycles per second, and a one or two stage amplifier 25 forsquaring the wave followed by a conventional pulse amplifier 28. Thesignal output of the last amplifier is applied, through the couplingcondenser 21, directly to the grid l5 of the impedance device. A diode28 and parallel resistor 29 are connected across the input of theimpedance device to hold constant the reference level of the pulses.

Now, a low pass filter 30 comprising the resistor II and the condenser32 is connected between the output of the amplifier I8 and the input ofthe impedance device, and the time con- 4 stant or cut-oflfrequency ofthe resistance-capacity combination is chosen intermediate the signalfrequency and the probable frequency of variation of the line voltage.Since voltage variations at the oscillator attributable to line voltagedisturbances and drift or due to load changes are usually quite low infrequency, the cut-off irequency may be made lower than any usablesignal frequency. Hence, all regenerative voltages of signal frequencymay be blocked by the low pass filter to permit signal modulation ofcurrent passed by the impedance device without altering the voltageregulating function of the device.

While the impedance of tube It has been described in series between thesource and the load, it will appear to those skilled in the art that theimpedance of the tube could be connected in shunt to the lines it and iI to perform the voltage regulating function. The phase of thedegenerative energy would of course then be reversed.

The functional relations of the reflector voltage, time, and amplitudeof oscillator output are depicted in the graphs of Fig. 2. The curve 33indicates how the high frequency output of a refiex oscillator drops offto zero as the reflector voltage varies to either side of the optimummode voltage VI. At other reflector voltages, such as V3, the oscillatorwill recommence oscillations. The direct current pulse voltagerepresented by the line 34 is applied to the grid of the impedancedevice and if adjusted to such a value as to repetitiously change thereflector voltage between the two values Vi and V2 corresponding,respectively, to reflector voltages for full-on and full-oiloscillations, pulses 35 of high frequency appear in the oscillatoroutput. If the pulse signals 34 are substantially square and the slopeof the sides of the pulses approach infinity, the frequency transitionof the oscillator becomes so short frequency modulation components maybe neglected. The envelope of the high frequency oscillator output isthen correctly represented by the rectangular forms 35. Modulation ofthe phase, frequency or duration of the direct current pulses produce,obviously, corresponding changes in the high frequency pulses.

While the modulated voltage regulator of this invention has beenspecifically applied to a reflex oscillator, it may be applied to moreconventional oscillators or to high frequency modulators where thereference voltage must be maintained as a predetermined value. Theterminals of my regulator may for example supply the steady voltage andthe signal to the anode or to the grid of a cotnventional feed-back orelectron-coupled oscilla or.

That is, while I have described the principles of my invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of my invention.

I claim:

1. In combination an unregulated direct current voltage source, a load,a grid-controlled electron discharge device, the anode-cathode space ofsaid device being connected between said source and said load, meansresponsive to voltage changes of said source applying a voltage to saidgrid to oppose current changes in said space, a signal source connectedto said grid, and a low pass filter with a cut-oi! frequency below thesignal frequency of said source connected between said grid and thevoltage responsive means.

2. The method of modulating a steady direct current comprising varyingthe impedance of the circuit between the current source and the load forsaid source in response to changes in voltage of said source of apredetermined range of frequencies, the impedance changes being of suchphase as to neutralize changes in magnitude of said direct current, andmodulating said impedance at signal frequencies outside saidpredetermined range of frequencies.

3. In combination, a voltage source, an electronic device connected tosaid source, said device being responsive to voltage variations of saidsource, an impedance device including an anode, a cathode and a grid,the anode and cathode being serially connected between said source andsaid electronic device, means applying degenerative energy to said gridfrom said source, and a signal source coupled to said grid.

4. In combination, a voltage source, an electronic device connected tosaid source, said device being responsive to voltage variations of saidsource, an impedance device including an anode, a cathode and a grid,the anode and cathode being serially connected between said source andsaid electronic device, means applying degenamplifier tube, the inputcircuit of said amplifier 85 voltage regulator inoperative to voltagechanges of signal frequency.

'7. In combination, a reflex oscillator containing a reflectionelectrode, a voltage source connected to said reflection electrode; avoltage regulator in circuit with said source responsive to voltagechanges at said reflection electrode, a signal source coupled to saidreflection electrode, and means to exclude signal voltage variationsfrom said voltage regulator.

THOMAS F. MARKER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,120,884 Brown June 14, 19382,393,785 Leeds Jan. 29, 1946 2,403,716 Goldberg et al July 9, 1946

